On Open MPI 1.2, I used following command to get the default host file:
ompi_info -a --parseable | grep rds_hostfile_path

Now, on Open MPI 1.3, the parameter does not seem to exist anymore. I
checked that there is another parameter
(mca:orte:base:param:orte_default_hostfile), but its value is always empty.

Which file whould I used for a system-wide default host file? Is there
another way to query the path for this default host file? Or is a
command to query which hosts are going to be used by mpi by default?